Speedometers, tachometers, and similar devices provide critical information to drivers of motor vehicles. Use of the information provided by such an instrument, however, requires an operator to divert attention away from the environment in which the vehicle is being operated. Although only momentary, it is better that an operator rarely, if ever, need to divert attention away from the environment since reference of the environment surrounding the motor vehicle is critical to safety of operation.
Various devices have been previously developed to address this general concern. Cruise control, for example, automatically regulates the speed of a vehicle's operation to a desired speed. Operation of the cruise control requires at least one glance away from the environment to set the desired speed. In addition, cruise control has limited utility in situations involving significant traffic where a steady cruising speed cannot be obtained. A head-up display is another effort to provide drivers information without requiring a diversion of attention away from the environment. These displays have found limited acceptance and use in practice, though. These two techniques also represent techniques which typically must be installed as original equipment, or added on at significant expense. This further limits their application in practice.
U.S. Patent No. 3,980,041 to Evans seeks to provide an add-on speedometer speed warning indicator which could be applied to the clear cover of a speedometer without disassembly of the speedometer. The Evans device is a plastic plate which adheres to the cover of a speedometer such that once a critical speed is reached further acceleration of the vehicle will cause the needle in the speedometer to be hidden from view. Though this device obviates the need to disassemble a speedometer for use of the device, it fails to solve the problem of diverting an operator's attention away from the vehicle's operating environment. In addition, adjustment of the device is rather cumbersome since it requires removal of a plate and replacement with a differently conFIGUREd, recut or repositioned plate.
Thus, there is a need for an add-on accessory which alerts an operator when a critical value is indicated by the output of an analog metering device without requiring the operator to look at the analog meter. Such an add-on accessory should be adjustable so that the operator may readily and conveniently select a desired critical value. Such a device is provided by the present invention.